When a caterpillar crawls, its internal organs slide forward inside its body before its legs move. Does that matter? It does if you’re a caterpillar, but it also does if you’re a designer of soft-bodied robots. A team of researchers working at Massachusetts' Tufts University used an X-ray to observe large, opaque-bodied caterpillars, then backed up their findings by examining smaller, translucent caterpillars under a microscope. In both cases, it was observed that the caterpillar’s internal center of mass moved forward first, while its middle legs remained attached to the substrate. In a paper on their findings, the team wrote that the so-called gut-slide is “unlike any form of legged locomotion previously reported and represents a new feature in our emerging understanding of crawling.”